Digital cameras often have problems when focusing on moving subjects or when people shake hands, for example. Auto-focus algorithms employed in auto-focus systems used in the cameras often miss intended focus, resulting in a blurred image. The focus failures are most prevalent when a user is panning the camera or the subject is moving, either of which appears as scene motion to the auto-focus system.
Digital camera focus algorithms often capture small focus images on a CCD array or sensor of the camera and then move the focus lens motor. A focus figure-of-merit is calculated for each of these “focus captures” which measures how in-focus a focus measurement (focus capture) is.
Motion of the camera or motion in the scene can cause the figure-of-merit to be incorrect when compared with previous focus measurements (focus captures). The focus figure-of-merit is very sensitive to scene motion because it typically relies on an edge detection scheme that requires edge content in the scene to remain constant.
It would be desirable to stabilize the auto-focus images so that the figure-of-merit can be computed for the scene that is more consistent between iterations of the auto-focus algorithm.